After pipe installation and bedding, backfilling of a trench often occurs in lifts. What is the primary reason for placing and compacting backfill material in layers of specific thickness, rather than dumping all at once?

Question: After pipe installation and bedding, backfilling of a trench often occurs in lifts. What is the primary reason for placing and compacting backfill material in layers of specific thickness, rather than dumping all at once?

Answer options:

• To reduce the overall time required for backfilling the entire trench.
• To allow for natural settlement of the soil over a longer period. ✅ To achieve specified compaction uniformly and prevent excessive settlement or voids.
• To accommodate different types of backfill material in distinct sections.

Correct answer: To achieve specified compaction uniformly and prevent excessive settlement or voids.

Explanation: Compacting backfill in lifts (layers) ensures that the material achieves the required density and avoids large voids beneath the surface. This prevents future settlement of the trench, which can cause damage to overlying structures or surfaces, as detailed in municipal and engineering specifications.